The Oxygen25 is a welcome addition to your studio! For the price, it delivers exactly what you need without many frills— 25 keys, octave control, pitch bend and modulation wheels, a volume slider, transport controls, and eight MIDI CC knobs. It's a fairly large controller for only having 25 keys (partially due to the fact that it has full-length keys instead of the common "mini keys"), so it's not the best solution for producers who also need a performance tool (even though Ean Golden famously used this controller with Traktor to DJ full sets), but it's right at home in a studio for sure.
I've been using this about every day since it was new (MK3) and it's been a while. Still, it hasn't degraded in usefulness or in wear and tear. Nowadays I'd go for something slimmer, maybe with some drum-pads integrated, but as a overall cheap, down to business, no-nonsense keyboard / controller I think it still shines more than many alternatives out there. Works flawlessly with both Ableton Live 9 and Reason 8! Had some trouble getting the "DirectLink" setup function with Cubase, but it's easy to use the midi-learn feature, so no real problems. I recommend it!
Mediocre at best. The keys on this thing feel like there's a layer of playdough underneath the keys so i guess you could say it has a squishy action. I'm unsure if this thing as aftertouch but I'm betting on no. either way, save your money and buy a better controller if you can afford it.